/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.iotdb.library.frequency.util;

import org.apache.iotdb.udf.api.collector.PointCollector;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Util for UDFFFT
 */
public class FFTUtil {
    private final String result;
    private final double compressRate;
    private static final Logger logger = LoggerFactory.getLogger(FFTUtil.class);

    public FFTUtil(String res, double cmprate) {
        this.result = res;
        this.compressRate = cmprate;
    }

    public void outputCompressed(PointCollector collector, double a[]) throws Exception {
        int n = a.length / 2;
        // calculate total energy
        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum += a[2 * i] * a[2 * i] + a[2 * i + 1] * a[2 * i + 1];
        }
        // compress
        double temp = a[0] * a[0] + a[1] * a[1];
        add(collector, a, 0);
        for (int i = 1; i <= n / 2; i++) {
            add(collector, a, i);
            temp += (a[2 * i] * a[2 * i] + a[2 * i + 1] * a[2 * i + 1]) * 2;
            if (temp > compressRate * sum) {
                if (logger.isDebugEnabled()) {
                    logger.debug(String.valueOf(i));
                }
                break;
            }
        }
        // sign at the tail for length
        add(collector, a, n - 1);
    }

    public void add(PointCollector collector, double a[], int i) throws Exception {
        double ans = 0;
        switch (result) {
            case "real":
                ans = a[i * 2];
                break;
            case "imag":
                ans = a[i * 2 + 1];
                break;
            case "abs":
                ans = Math.sqrt(a[i * 2] * a[i * 2] + a[2 * i + 1] * a[2 * i + 1]);
                break;
            case "angle":
                ans = Math.atan2(a[2 * i + 1], a[2 * i]);
                break;
            default:
                throw new Exception("It's impossible");
        }
        collector.putDouble(i, ans);
    }

    public void outputUncompressed(PointCollector collector, double a[]) throws Exception {
        int n = a.length / 2;
        for (int i = 0; i < n; i++) {
            add(collector, a, i);
        }
    }
}
